The present invention relates to the general field of water filtering systems used in a fish rearing environment and more specifically to such systems in which solid wastes, ammonia and other organic impurities harmful to fish are present and need to be eliminated on a continuing basis from a container or tank remote from the location of the fish.
The vast majority of conventional filtering systems are employed in the same locations as the fish and as a result the filter media is placed either on the bottom of the tank or pond or otherwise maintained beneath the water area in which the fish live. In this type of a fish rearing environment it is the general practice to wash the filter media by using upward flow of fluid cleansing action. Such method suffers the disadvantage of the accumulated solid wastes being carried upward and into the area in which the fish are located, resulting in increased pollution of the water and increased difficulty in capturing and removing such waste. In fish rearing water filtering systems of the type that is located in a tank remote from the fish rearing environment and in which the water is continually circulated between the two locations, it is possible to avoid the above-mentioned disadvantage. Conventional systems of this type are exemplified by U.S. Pat. Nos. 3,842,804 and 3,886,902, wherein the influent and effluent are separated by the filter media and the fluid flow during the filtering process is continuous and always in the same direction. Such systems are generally inefficient, requiring large capacity tanks and long periods of time to accomplish the desired water purification because the filter media is not used to its best advantage. Specifically, in these types of water filter systems the effectiveness of the filter media in supporting the bacteria necessary to ingest and oxidize the impurities (such as ammonia) is poor because only the first layers of the exposed side of the filter media receives the high concentration of organic-laden water. The later-exposed layers of the filter media are therefore less effective in providing an environment for bacteria growth.
The use of filter media consisting of buoyant plastic rings, each having a diameter of 31/2 inches is known. In a tank having a filter plan area of 300 square feet, a minimum six-foot filter media depth is required to provide the necessary removal of all ammonia and other impurities in the water. For practical and economical reasons, such depth requirement is not feasible.